In the Fischer-Tropsch reaction synthesis gas is reacted in the presence of a heterogeneous catalyst to give a hydrocarbon mixture having a relatively broad molecular weight distribution. This product comprises predominantly straight chain saturated hydrocarbons which typically have a chain length of more than 5 carbon atoms. Similarly synthesis gas may be reacted in the presence of a heterogeneous catalyst to give oxygenates e.g. methanol or dimethyl ether.